removed svn_prompt_info from prompt in an effort to speed things up
Created new, streamline theme for zsh prompt. Changed zshrc to use new theme.

Created cello.zsh-theme file, which creates an identical prompt to zanshin.zsh-theme
except that cello theme doesn't display repository information for hg or svn repos.
Hope is that new session startup times will be reduced.

Modified zshrc file to utilize new theme.
added comment about oh-my-zsh dependency